Beware black ice, frozen foliage as cold snap comes to Bay Area

A dense cold front muscled its way into the Bay Area on Wednesday, shoving warm air out of the way and settling in for a stay into next week, potentially reintroducing residents to black ice on the roads and frozen foliage in the garden.

Forecasters said temperatures throughout the Bay Area are expected to drop to freezing and lower, and could set records -- including one in San Jose that goes back to the 19th century.

"Everybody's going to get their share," said National Weather Service forecaster Diana Henderson. "It's coming down out of the north -- that's where all the cold is, and we usually like to keep it up there. But every once in a while a burst of really cold air migrates down."

San Jose can expect to see temperatures drop to 38 by Thursday morning, and touch the 32-degree freezing point by the weekend. Further south, Morgan Hill will be a couple degrees cooler, and the snap could break a 28-degree record for Saturday in San Jose that has stood since 1894, Henderson said.

Areas in the East Bay could reach that San Jose record, Henderson said.

Outlying areas like Concord and Livermore will see nightly temperatures sink to 27 to 29 degrees into the weekend before temperatures start to get slightly "warmer" and go back up to the mid to high 30s at night.

Days will warm up to the low 50s in the South Bay, Henderson said, while East Bay temperatures will hover right around the high 40s and possibly crack the 50 degree mark. Normal Bay Area temperatures for this time of year are about 10 degrees higher than what's been forecast.

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Snow level are also expected to drop to extremely low elevations over the next few days.

Though rain levels will total less than half an inch at best, according to Henderson, snow could fall as low as 1,500 feet, and up to a half a foot of snow in certain mountainous areas.

But enough snow along with freezing temperatures will cause slow travel for at time along Interstate 80 over Donner Pass and parts of Interstate 5.

The California Highway Patrol issued a warning Wednesday that the conditions are conducive to black ice, hard-to-see patches of frozen water on roadways.

"If the roadway appears wet, however, there is no spray coming from the vehicles' tires around you, be aware," CHP officials said in advisory released Wednesday. "This could be extremely dangerous. You may be driving on ice."

Bill Miller of Gilroy's Bonfante Nurseries said that in addition to citrus trees, residents should be wary of the freeze effect on other tropical specimens such as ficus, carob and jacaranda trees.

"If it's too big to cover with cloth, people can wet down the soil to insulate the roots," Miller said. "If it's bone dry it lowers the insulation factor."

A cyclist rides on the American River Parkway bike trail near Sacramento on Jan. 8, 2013. (AP Photo/The Sacramento Bee, Tim Reese)

Henderson said the front doesn't have much moisture, and residents may see only "drips and drabs" of rain, although she said it's possible that higher peaks such as Mount Hamilton might see some snow.

Jennifer Van Every, spokeswoman for EHC LifeBuilders, said they "definitely expect an uptick" of people utilizing their cold-weather shelters in San Jose, Sunnyvale and Gilroy.

"That's the norm; you see it for both very cold temperatures and rain," she said. "We're always encouraging people to get out of the cold."

Henderson said the cold air will move out of town slowly, and by next Wednesday temperatures should be rising to more normal levels.